feat: extract JS browser runtime from feat/js-browser-runtime

- Update el-compiler/src/codegen-js.el to Phase 5 (1245 lines, up from 926)
  Adds: lambda literals, try/catch, extern fn, JS method call, Promise helpers,
  Object/Array utils, URL import declarations
- Update el-compiler/runtime/el_runtime.js (1049 lines, up from 679)
- Add examples/browser-counter.el, examples/browser-auth.el
- Update spec/codegen-js.md to Phase 5 status
- Update el-compiler/src/compiler.el: add --bundle, --minify, --obfuscate flags,
  bundled IIFE mode, terser/javascript-obfuscator post-processing pipeline
- No lexer.el or parser.el taken from this branch

examples/browser-counter.el

@@ -0,0 +1,41 @@
+// browser-counter.el — canonical browser DOM bridge example
+//
+// Compile with:  elc --target=js examples/browser-counter.el > counter.js
+//
+// Then include in an HTML page that has a <span id="count-display"> element.
+// The page can call window.increment() from any onclick handler, e.g.:
+//   <button onclick="increment()">+1</button>
+//
+// On load the display is initialised to "0".  Each call to increment()
+// adds 1 and updates the display text.
+//
+// Demonstrates:
+//   - dom_get_element   to locate a DOM node by id
+//   - dom_set_text      to update visible text content
+//   - dom_is_null       to guard against missing elements
+//   - window_set        to expose an El function for inline event handlers
+//   - state_set/get     for in-memory counter state (survives calls, resets
+//                       on page reload — same semantics as the C state_* API)
+
+fn init() -> Void {
+    state_set("counter", 0)
+    let display = dom_get_element("count-display")
+    if !dom_is_null(display) {
+        dom_set_text(display, "0")
+    }
+}
+
+fn increment() -> Void {
+    let current = str_to_int(state_get("counter"))
+    let next = current + 1
+    state_set("counter", next)
+    let display = dom_get_element("count-display")
+    if !dom_is_null(display) {
+        dom_set_text(display, int_to_str(next))
+    }
+}
+
+fn main() -> Void {
+    init()
+    window_set("increment", increment)
+}